Apparatus for calibrating thermostatic switches

ABSTRACT

To calibrate a normally-closed thermostatic switch of the type having a bimetallic switch arm fastened at one end to the inside of the switch housing, the switch is placed in an oven beneath reciprocable calibrating tool with the switch arm connected in circuit with the tool operation means. When the switch reaches the temperature at which it is intended to open, the tool is lowered so that a pair of projections on its lower end deform the housing at two spaced points until the switch arm snaps to its open position, simultaneously terminating the calibrating operation and deenergizing the tool actuating means.

United States Patent 1151 3,683,654 Hire [45] Aug. 15, 1972 [5 APPARATUS FOR CALIBRATING 1 r n s Cit d THERMOSTATIC SWITCHES UNITED STATES PATENTS 1 lnvemeri Charles John "ire, Pittsferd, 2,859,608 ll/l958 Bear et al. ..73/1 t 3,141,322 7/1964 Himelsbaugh ..73/1 [73] Ass'gnee' Cmbmam weslesichem $223,808 12/1965 Wehl ..337/94 Utrecht, Netherlands [22] Filed: Jan. 25, 1971 Primary ExaminerLowell A. Larson 1 pp NO: 109,192 Attorney-Schlesmger, F1tzs1mmons & Schlesmger Related us. Application Data [57] ABSTRACT To calibrate a normally-closed thermostatic switch of [62] Dmsion of 1969 the type having a bimetallic switch arm fastened at one end to the inside of the switch housing, the switch is placed in an oven beneath reciprocable calibrating Cl 1 1 13/116 tool with the switch arm connected in circuit with the 72/478 tool operation means. When the switch reaches the [51] Int. Cl. ..B2ld 53/00 temperature at which it is intended to open, the tool is [58] Field of Search ..72/30, 413, 47s; 337/89, 94, lowered 89 that a P of projections 99 its lower end 337/347, 360, 368; 113/116 GG;'29/593, 622; 73/1 F deform the housing at two spaced points until the switch arm snaps to its open position, simultaneously terminating the calibrating operation and deenergizing the tool actuating means.

7 Claims, 4 Drawing Figures Patented Aug. 15, 1972 3,683,654

FIG. 3

INVENTOR.

2O 26 18 CHARLES JOHN HIRE BY Fl 4 r ATTORNEYS APPARATUS FOR CALIBRATING THERMOSTATIC SWITCHES This application is a division of my copending U. S. patent application Ser. No. 878,767, filed Nov. 2l, 1969, now U.S. Pat. No. 3,587,022. It relates to sealed thermostatic switches, and more particularly to apparatus for calibrating thermostats of the type having current carrying switch arms of the bimetallic, snap-action type.

Thermostats employing snap-action, current-carrying actuators or switch arms are particularly useful as electric motor protectors to prevent undesirable overheating of the motors. When used for this purpose, the snap-action switch arm of the thermostat is normally disposed in closed position to conduct current to the motor. When the ambient temperature rises above a predetermined value, however, as a result, for example, of an excessive flow of current in the motor windings, the thermostatic switch arm snaps suddenly open to deenergize the motor.

Although with known techniques it is possible to design this type of thermostat so that, as assembled, its switch arm will open when its ambient temperature approximates a preselected value, most such switches can be rendered accurate only by calibrating them after they have been assembled and sealed. With prior calibrating techniques, however, less than half of the switches operate with satisfactory accuracy, and as a consequence, most switches are not usable for the purpose intended.

It is an object of this invention to provide improved apparatus for calibrating thermostats of the type described, and which will substantially reduce the number of thermostats which must be rejected after calibration.

A further object of this invention is to provide a novel tool for calibrating switches of the type described.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawing.

In the drawing:

FIG. 1 is a side elevational view of a normally-closed thermostat or temperature-responsive switch of the type that is adapted to be calibrated by apparatus made in accordance with this invention, the switch being illustrated as it appears before being calibrated, and with parts thereof cut away and shown in section;

FIG. 2 is a plan view of this switch before calibration with portions thereof cut away for purposes of illustration;

FIG. 3 is a schematic view illustrating diagrammatically one method employed in calibrating a switch of this type; and 4 FIG. 4 is a fragmentary side elevational view of the calibrated switch and calibrating apparatus thereof made in accordance with one embodiment of this invention, and illustrating schematically electrical control means for manipulating the novel calibrating tool which forms part of this apparatus.

Referring now to the drawing by numerals of reference, and first to FIGS. 1 and 2, l denotes a thermostat, or temperature-responsive switch comprising an inverted, generally oblong-shaped housing 12 having around its lower, open end an integral flange 14,

which projects laterally both at opposite sides and ends of the main body of the housing. Integral with, and projecting beyond the flange 14 at its left end in FIGS. 1 and 2 is a terminal 15. This terminal, which is laterally offset to one side of the centerline of the housing 12, is formed with initially spaced, parallel legs 16, which are adapted to be crimped over an electrical conductor (not illustrated) to form an electrical connection with housing 12. The lower, open end of housing 12 is sealed by a flexible gasket, or layer of dielectric tape 18, the marginal side edges of which are folded as at 19 upwardly, and over the longitudinal side edges of the flange 14. This tape or gasket 18 may be made of a polyester film such as Mylar.

Mounted beneath the gasket 18 is an elongate, generally flat metal plate or conductor 20, the longitudinal side edges of which are bent or folded as at 21 up wardly and over the folded side. edges 19 of the gasket 18 thereby to secure the plate 20 and the gasket 19 sealingly over the bottom open end of the housing 12. At the left end'thereof in FIGS. 1 and 2 the plate 20 also has an integral, laterally ofiset terminal 23, which projects beyond the plate in laterally spaced relation to the terminal 15, and which has initially spaced legs 24 that are adapted to be crimped over one end of a conductor (not illustrated) electrically to connect the latter to a plate 20. Adjacent its opposite end the plate 20 carries a contact 26, which projects upwardly through a registering opening in gasket 18, and into the lower or open end of the housing.

Adjacent one end thereof the housing 12 has an inwardly-projecting dimple 30, which has a flat underside. Fixed at one end to the underside of dimple 30 in electrical contact with the housing 12, and extending at its opposite end over the upper surface of stationary contact 26 is a flexible, temperature-responsive, bimetallic switch arm 32. At its free end arm 32 carries a contact button 33, which, at room temperature, is

normally held in engagement with contact 26 to close the circuit between terminals 15 and 23.

As thus far described, switch 10 is illustrative of a normally-closed thermostat as it appears after assembly, and prior to calibration. Before it is ready for use, however, the switch 10 of FIGS. 1 and 2 must be calibrated to snap to its open position when the ambient temperature is above some predetermined value. To effect this calibration in production, each of a plurality of such switches 10 is advanced in single file by a grounded metal conveyor 40 (FIGS. 3 and 4) through an oven A, the interior of which is maintained at a constant temperature, for example 295 F, which corresponds to the temperature at which it is desired that each arm 32 snap open.

Mounted in the oven A to reciprocate vertically above the conveyor 40 and the thermostats carried thereby is a cylindrical, vertically disposed tool 42 (FIGS. 3 and 4). On its lower end tool 42 has a reduced-diameter cylindrical projection 43, which is offset from the centerline of the tool, and which has a diameter approximately equal to the desired inside diameter of the dimples 30 in the switches 10 that are to be calibrated. Threaded at its upper end in an internally threaded blind bore 44 in the lower end of tool 42 is a pin 45, which is disposed in parallel, offset relation to the axes of tool 42 and cylindrical projection 43. Pin

to the temperature of the oven i.e., 295F in the case illustrated.

As each switch moves into registry with the lower end of the tool 42, a probe or contact 48 in the oven engages one of the legs 16 of the terminal on the switch. The contact 48 is designed to connect the arm 32 of each switch 10 in circuit with an electricallyoperated device, which controls the movement of tool 42. This device may include, for example, a relay 49, the operating coil of which is connected at one side to a power supply P, for example a battery, and at its opposite side through the probe 48, one of the legs 16, tenninal 15, housing 12, bimetallic switch arm 32, contacts 33 and 26, and plate and metal conveyor 40 to ground.

Thus as each normally-closed switch 10 moves beneath the tool 42, the relay 49 is energized, and actuates a conventional step-by-step drive means, which is connected to the externally threaded upper end of the tool 42. By way of example, the upper end of tool 42 may be threaded into a central bore formed in a ratchet wheel 35, which is mounted above oven A to be rotated intermittently by a pawl 36. This pawl may be carried by an operating arm 37, which is reciprocated upon energization of relay 49. The tool 42 is thus lowered step-by-step in increments of approximately 0.0005 inch so that the projection 43 on the lower end of the tool will press into the dimple 30 in the top of the registering switch 10, and at the same time, the pointed end 46 of pin 45 will be pressed against the top of the housing 12 of the switch to form therein a further, smaller dimple 50 having a pointed underside positioned to engage the upper surface of the arm 32 of the thermostat between its fixed and free ends, and substantially medially of its longitudinal side edges.

The tool 42 continues to descend until the free end of the bimetallic arm 32 snaps upwardly from its closed position (FIG. 4) to its open position. When this occurs, the circuit energizing the coil of the relay 49 is broken; and the drive device for tool 42 is deenergized or released. The thermostat will now have been calibrated to open at 295F. A spring-return, or the like, (not illustrated) then causes the tool 42 to be shifted upwardly to its inoperative, start position to disengage the lower end of the tool from the nowcalibrated switch 10, so that the conveyor may advance the next switch 10 beneath the tool. The probe 48 then engages one of the legs on the tenninal 15 of this next switch to begin the calibration of this next switch.

After being calibrated, the switches are moved successively by conveyor 40 out of oven A, and successively through a plurality of additional ovens where the calibrated switches are tested in known manner to determine whether or not they will reclose properly within a predetermined ambient temperature range below the temperature of the oven A; and whether or not they will properly reopen when once again elevated to the calibrating temperature of 295F. Switches which do not meet this requirement are rejected.

It has been customary in the past to calibrate thermostats or switches of the type described by bringing the switches up to a temperature corresponding to the ambient temperature at which they should open, and then deforming the switch housing at a single point until the temperature-responsive arm, for example arm 32, snaps from its closed to its open position. Applicants tool 42, on the other hand, deforms the switch housing 12 at two spaced points, one of which registers with the fixed end of the arm 32, and other of which re gisters with the free portion of the arm at a point spaced between the fixed and free ends thereof. By maintaining a precise relationship between the projection 43 and the pin 45, it has been found that the yield of properly calibrated switches has increased to close to percent, as compared to a 40 percent yield that was realized when the switch housings were deformed at a single point. In practice, the pin 45 is usually secured in an adjusted position in which its lower end projects slightly beneath the lower end of the projection 43; and the distancex(FIG. 4) separating the axial centerlines of the projection 43 and pin 45 is maintained so that the dimple 50 will engage the associated switch member 32 at a point rearwardly of the midpoint of the free portion of the arm.

It will be apparent that the tool 42 and associated apparatus described herein enable a substantial increase in the percentage of acceptable, properly calibrated temperature-responsive switches of the type described, as compared with prior conventional calibrating apparatus. Moreover, the stresses, which are set up in the switch housing as a result of deformation by the tool 42, minimize undesirable creep and consequent erratic operation of the bimetallic switch arms 32. Further, the dimple 50, that is formed in each switch housing 12 by the pin 45, operates as a fulcrum for the bimetallic switch arm 32, thus producing a more reliable snap-action of the arm when the arm is brought to switch-opening temperature. Moreover, by incorporating each switch arm 32 in the control circuit of the means which actuates the tool 42, the deforming operation is auto matically stopped the moment that the arm 32 swings from its closed to its open position. Also, since the tool 42 is lowered slowly and intermittently during the calibration of the switch, the deformation takes place under almost static loading conditions, thus minimizing the chance of the switch arm 32 being accidentally snapped to its open position as the result of dynamic or shock loading of the housing. Also, the depth of the dimple 50 obviously can be controlled merely by threadably adjusting pin 45 in bore 44 better to enable more precise calibration of the switches.

Having thus described my invention, what I claim is:

1. Apparatus for calibrating a thermostat of the type having a metal housing containing a normally-closed, snap-action type, bimetallic switch arm which is fixed at one end to the inside of said housing comprising a tool mounted for vertical reciprocation,

drive means for imparting movement to said tool in one direction of its reciprocable movement,

means for supporting said thermostat with said housing positioned beneath and confronting the lower end of said tool, and

a pair of spaced projections extending from said lower end of said tool to engage and deform said housing inwardly at the point where said one end of said arm is fixed and at a point spaced therefrom, when said tool is moved in said one direction.

2. Apparatus as defined in claim 1, wherein one of said projections comprises a cylindrical boss having a plane undersurface, and

the other of said projections comprises a pin adjustably mounted at its upper end in the lower end of said tool, and having a pointed end projecting beneath said tool beyond said cylindrical boss.

3. Apparatus as defined in claim 2, wherein said tool is cylindrical, and

the axial centerlines of said boss and of said pin are disposed in laterally offset parallel relation to one another and to the axis of said tool.

4. Apparatus as defined in claim 3, including an oven, and

a conveyor for advancing a plurality of said thermostats slowly through said oven to heat the thermostats to a predetermined temperature,

said tool being mounted in said oven to recip-rocate into and out of engagement with each thermostat passing through said oven, and

said pin being adjustably threaded in the lower end of said tool to permit adjustment of said pointed end vertically relative to said cylindrical boss.

5. Apparatus as defined in claim 1, wherein said arm is connected in electrical circuit with said drive means so that when said switch arm opens, said drive means is interrupted to stop the movement of said tool in said one direction.

6. A tool for deforming the housing of a thermostat to calibrate the thermostat, comprising a punch bit having two spaced projections on its operating end.

7. A tool as claimed in claim 6, wherein the projections are parallel, and one of them is adjustable in the bit relative to the other to extend said one projection beyond the other.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 683,654 Dated August 15, 1972 Inventor(s) Charles John Hire It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page, in section [73] cancel "Combinatle Weslesschelde v.0. f. Urecht, Netherlands" and substitute Fasco Industries, Inc., Rochester, N.Y..

Signed and Scalzd this mm Day of September 1902 [SEAL] Artur:

GERALD J. MOSSINGHOFF Arresting Officer Commissioner of Patents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE .OF' CORRECTION Patentlkn Q ','D; ed August 15, 1972 Invmumr(s) Charles Jhn,Hir

It is certified that effor appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The assignee of this patent-is Fasco Industries, Inc. Rochester, New York, not.Combinatie weslesschelde v.o.f., Ultrecht, Netherlands. a 1

The attorney is Shlesinger, Fitzsimmons & Shlesi v nger, hot Schlesinger, Fizsimmons'& Schlesinger.

Signed and seaieo this l7th day of April 1973;

(SEAL) Attest:

EDWARD M.FLETCHER,JR,. GOTTSCHALK Attesting Officer I H Commissioner of Patents ORM PO-KOEO (10-69) USCOMM-DC 6O376-P69 U.S. (SIVIRNMENT PRINTING OFFICE: LS! 0-366-331 

1. Apparatus for calibrating a thermostat of the type having a metal housing containing a normally-closed, snap-action type, bimetallic switch arm which is fixed at one end to the inside of said housing comprising a tool mounted for vertical reciprocation, drive means for imparting movement to said tool in one direction of its reciprocable movement, means for supporting said thermostat with said housing positioned beneath and confronting the lower end of said tool, and a pair of spaced projections extending from said lower end of said tool to engage and deform said housing inwardly at the point where said one end of said arm is fixed and at a point spaced therefrom, when said tool is moved in said one direction.
 2. Apparatus as defined in claim 1, wherein one of said projections comprises a cylindrical boss having a plane undersurface, and the other of said projections comprises a pin adjustably mounted at its upper end in the lower end of said tool, and having a pointed end projecting beneath said tool beyond said cylindrical boss.
 3. Apparatus as defined in claim 2, wherein said tool is cylindrical, and the axial centerlines of said boss and of said pin are disposed in laterally offset parallel relation to one another and to the axis of said tool.
 4. Apparatus as defined in claim 3, including an oven, and a conveyor for advancing a plurality of said thermostats slowly through said oven to heat the thermostats to a predetermined temperature, said tool being mounted in said oven to recip-rocate into and out of engagement with each thermostat passing through said oven, and said pin being adjustably threaded in the lower end of said tool to permit adjustment of said pointed end vertically relative to said cylindrical boss.
 5. Apparatus as defined in claim 1, wherein said arm is connected in electrical circuit with said drive means so that when said switch arm opens, said drive means is interrupted to stop the movemeNt of said tool in said one direction.
 6. A tool for deforming the housing of a thermostat to calibrate the thermostat, comprising a punch bit having two spaced projections on its operating end.
 7. A tool as claimed in claim 6, wherein the projections are parallel, and one of them is adjustable in the bit relative to the other to extend said one projection beyond the other. 